The present invention concerns an access network for mobile terminals of the type which consists of a switching circuit connected, on the one hand, to at least one other external network and, on the other hand, to a local access network which is itself connected to a number of radio terminals, each terminal being provided for communicating with mobile terminals.
The present invention falls within the framework of access networks for mobile units based on the ATM (Asynchronous Transfer Mode) technology. More precisely, it concerns access networks for mobile units which are based on the end-to-end ATM technology, both at the control level and the user level. Consequently, the mobile terminals envisaged in the present invention support applications which justify the use of this ATM technology provided for the transfer of data at increased flow rates. Among these applications, the following could be cited by way of example: videophony, data transmissions at high rates of flow, consulting Internet servers, etc.
In known mobile access networks, the ATM technology is only intended for access to the radio terminal, still called base station. In these known networks, the mobile terminals are unable to support protocol cells which are specific to this ATM technology, namely level 2 security protocols such as the standard protocol SSCOP and the set-up/release protocols such as the standard protocol Q2931. Also, the field of application in this case is generally cellular radio communication networks.
In a wideband network such as the ATM-type network, the signalling connections are secured at level 2 by a security protocol like the standard one called SSCOP. Thus, the routing of messages signalling the set-up/release of connections at the user level, as those sent by the standard protocol Q2931, supposes then the prior establishment of a level 2 connection.
It will be recalled that the SSCOP protocol ensures, in particular, the securing of signalling connections and permanently controls the integrity of the connections between the terminals MT and switching circuit VCX.
In the case of a network for stationary terminals, the virtual connection which transmits the cells of signalling messages between a terminal and its connecting switching circuit is permanent so that the security protocol SSCOP is automatically released as soon as the terminal is switching circuited on and it permanently controls the integrity of the connections established between the switching circuit and the terminal, even if no data is exchanged at the user level. Thus, these connections secured by the implementation of the SSCOP protocol are only cut off when the terminal or the switching circuit are switched off or, perhaps, when the physical connection between the terminal and the switching circuit is cut.
In the case of a network for mobile terminals, the maintenance of such a virtual connection cannot be permanently assured to the extent where it uses radio resources and the fact that the latter are scarce and costly.
Moreover, a local access network for mobile terminals ATM has, vis-à-vis access networks for stationary terminals, differences which raise specific problems, in particular when signalling procedures are implemented. These problems are noted below.
In addition to processing calls by the switching circuit, a network for mobile terminals integrates the set-up and release functions for internal virtual connections and reserves ATM resources and radio resources. These operations are managed call by call.
Moreover, incoming partial calls when a terminal of network can be called by another terminal using a localization procedure or paging the terminal called by broadcasting a request through all the mobile terminals located in the area covered by the network.
The object of the present invention is to propose an access network for mobile terminals in which the connections for the transmission of security messages sent by the SSCOP security protocol are managed on request, i.e., only for the duration of the communications. Moreover, a network of this type solves the aforementioned problems.
To this end, an access network for mobile terminals according to the invention is characterized therein that the protocols for establishing and releasing signalling channels and user channels between said switching circuit and a terminal and the security protocols of said channels are implemented only at the level of said switching circuit and said terminals, by exchanging signalling messages between them and therein that it comprises an adaptation server which is provided for intercepting messages sent by said signalling protocols in a transparent manner, and to implement, dependent on the contents of said intercepted messages, management protocols of said local access network in order to set up and release the signalling channels and the user channels in said local access network and to reserve the corresponding radio resources for them.
According to another characteristic of the invention, when the switching circuit receives a request for a connection with a terminal which is located in the area covered by said network, a terminal paging procedure is initiated by said adaptation server to which the said terminal responds by reserving the radio resources required for the signalling traffic and by sending an acknowledgement message, said server then determining the identifiers of a signalling channel in said local access network and establishing said signalling channel.
According to another characteristic of the invention, when said switching circuit receives a request for a connection with a terminal which is in the area covered by said network, it sends a release message of the security protocol, the interception of which by said server releases said terminal paging procedure, said terminal transmitting an acknowledgement message when said signalling channel is set up between the said terminal and said switching circuit.
According to another characteristic of the invention, if the switching circuit has not received the acknowledgement message after a set time has expired, it sends a new release message for the security protocol, the number of times that the switching circuit resends the release messages for the security protocol being limited, for example, to five.
According to another characteristic of the invention, it comprises a server through which all the signalling messages pass to the said switching circuit, the said server, on receipt of a message requesting a connection with a terminal which is within the area covered by said network, transmitting to the server a message so that it releases said terminal paging procedure, said terminal transmitting an acknowledgement message when said signalling channel is set up between said terminal and said switching circuit.
According to another characteristic of the invention, when a terminal is in the area covered by said network makes a call, it reserves the radio resources necessary for the signalling traffic and sends a message requesting a connection to the single adaptation server which then determines the identifiers of a signalling channel in said local access network and sets up said signalling channel.
According to another characteristic of the invention, said message contains the temporary logical address which was assigned to said terminal when it was in the dormant state in the area covered by said network, said server, on receipt of said message, establishing an agreement between said address and said identifiers of said signalling channel.
According to another characteristic of the invention, at the end of the establishment of said signalling channel, said signalling protocol for the security of the connection between the switching circuit and said terminal is released.
According to another characteristic of the invention, once the signalling channel has been set up in said local network and after the release of the security protocol, the protocol for establishing the connection at the user level is implemented, the adaptation server intercepting the messages sent by said protocol in order to reserve the radio resources required for the user traffic and set up a user channel in said local access network.
According to another characteristic of the invention, said local access network consists of a distribution network connected, for its connection to the switching circuit, to a virtual path mixer, said adaptation server being shunt-connected with said mixer in such a way that only the cells having the identifiers of the specific channels or the identifiers of the signalling channels in their heading at the level of said switching circuit or at the level of said terminals, pass through the adaptation server.
According to another characteristic of the invention, a permanent point-to-point channel is established between each of the terminals and the adaptation server for transmitting cells bearing said message for requesting a call coming from said calling terminal which is in the area covered by the corresponding terminal or the cells having a terminal-paging acknowledgement message.
According to another characteristic of the invention, between the adaptation server and each terminal, a permanent virtual path is established for the transmission of cells bearing the acknowledgement for the signalling channel set-up, said cells having an identifier of the virtual circuit equal to the identifier of the virtual circuit of said signalling channel.
According to another characteristic of the invention, a permanent point-to-multipoint channel is set up between the adaptation server and the terminals of said network for broadcasting the terminal-paging message.
According to another characteristic of the invention, when said adaptation server intercepts a release message coming either from the switching circuit or a terminal, it orders the release of the partial connections in the local access network and radio resources.
According to another characteristic of the invention, it comprises means for concealing, for a preset period of time, the release messages of the security protocol sent by switching circuit or a terminal when the release of the signaling channel has taken place.